Ensure that trusted PTR_TO_BTF_ID accesses perform PROBE_MEM handling in
raw_tp program. Without the previous fix, this selftest crashes the
kernel due to a NULL-pointer dereference. Also ensure that dead code
elimination does not kick in for checks on the pointer.
Reviewed-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
---
.../bpf/bpf_testmod/bpf_testmod-events.h | 8 +++++
.../selftests/bpf/bpf_testmod/bpf_testmod.c | 2 ++
.../selftests/bpf/prog_tests/raw_tp_null.c | 25 +++++++++++++++
.../testing/selftests/bpf/progs/raw_tp_null.c | 32 +++++++++++++++++++
4 files changed, 67 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/raw_tp_null.c
create mode 100644 tools/testing/selftests/bpf/progs/raw_tp_null.c
diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
index 6c3b4d4f173a..aeef86b3da74 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
@@ -40,6 +40,14 @@ DECLARE_TRACE(bpf_testmod_test_nullable_bare,
TP_ARGS(ctx__nullable)
);
+struct sk_buff;
+
+DECLARE_TRACE(bpf_testmod_test_raw_tp_null,
+ TP_PROTO(struct sk_buff *skb),
+ TP_ARGS(skb)
+);
+
+
#undef BPF_TESTMOD_DECLARE_TRACE
#ifdef DECLARE_TRACE_WRITABLE
#define BPF_TESTMOD_DECLARE_TRACE(call, proto, args, size) \
diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
index 8835761d9a12..4e6a9e9c0368 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
@@ -380,6 +380,8 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
(void)bpf_testmod_test_arg_ptr_to_struct(&struct_arg1_2);
+ (void)trace_bpf_testmod_test_raw_tp_null(NULL);
+
struct_arg3 = kmalloc((sizeof(struct bpf_testmod_struct_arg_3) +
sizeof(int)), GFP_KERNEL);
if (struct_arg3 != NULL) {
diff --git a/tools/testing/selftests/bpf/prog_tests/raw_tp_null.c b/tools/testing/selftests/bpf/prog_tests/raw_tp_null.c
new file mode 100644
index 000000000000..6fa19449297e
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/raw_tp_null.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+
+#include <test_progs.h>
+#include "raw_tp_null.skel.h"
+
+void test_raw_tp_null(void)
+{
+ struct raw_tp_null *skel;
+
+ skel = raw_tp_null__open_and_load();
+ if (!ASSERT_OK_PTR(skel, "raw_tp_null__open_and_load"))
+ return;
+
+ skel->bss->tid = sys_gettid();
+
+ if (!ASSERT_OK(raw_tp_null__attach(skel), "raw_tp_null__attach"))
+ goto end;
+
+ ASSERT_OK(trigger_module_test_read(2), "trigger testmod read");
+ ASSERT_EQ(skel->bss->i, 3, "invocations");
+
+end:
+ raw_tp_null__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/raw_tp_null.c b/tools/testing/selftests/bpf/progs/raw_tp_null.c
new file mode 100644
index 000000000000..457f34c151e3
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/raw_tp_null.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+int tid;
+int i;
+
+SEC("tp_btf/bpf_testmod_test_raw_tp_null")
+int BPF_PROG(test_raw_tp_null, struct sk_buff *skb)
+{
+ struct task_struct *task = bpf_get_current_task_btf();
+
+ if (task->pid != tid)
+ return 0;
+
+ i = i + skb->mark + 1;
+ /* The compiler may move the NULL check before this deref, which causes
+ * the load to fail as deref of scalar. Prevent that by using a barrier.
+ */
+ barrier();
+ /* If dead code elimination kicks in, the increment below will
+ * be removed. For raw_tp programs, we mark input arguments as
+ * PTR_MAYBE_NULL, so branch prediction should never kick in.
+ */
+ if (!skb)
+ i += 2;
+ return 0;
+}
--
2.43.5
